Nothing more frustrating that starting/stalling problems....especially when the volvo dealer has no fault codes.....

Problem sounds like the Cam Sensor, but there should be codes for that one...the fact that car wont respond to your pushing the gas peddle in makes me think you should check to make sure your air intake hose clamps are all tight and there are not cracks or leaks in any air ducts from the air cleaner to the throttle body and check the flame trap to make sure it's not plugged. Also check to make sure no vacuum lines are cracked, broken or unplugged.....

Haynes book also describes your problem in the section dealing with the fuel vapor canister....you might want to take a look at it to make sure no vacuum lines or fuel lines have come loose....(drivers wheel well area)